This invention relates to thermoplastic polyolefin (TPO) compositions. In one aspect, the invention relates to compositions comprising at least one polypropylene and at least one ethylene copolymer while in another aspect, the invention relates to compositions in which the ethylene copolymer is of low crystallinity. In still another aspect, the invention relates to compositions in which the xcex1-olefin of the copolymer comprises at least four carbon atoms. In yet another aspect, the invention relates to articles manufactured from the compositions.
Soft touch applications such as automotive overshoot parts (e.g., door handles and skins such as dashboard, instrument panel and interior door skins), tooth brush handles, grips, shoe soles, and toys, are requiring ever more flexible TPO compositions. The TPO compositions presently used for soft touch applications comprise a polypropylene and a nearly amorphous ethylene/propylene (EP) or an ethylene/propylene/diene monomer (EPDM) rubber. The EP and EPDM rubbers, which have relatively high glass transition temperatures (Tg) and are blocky (i.e., the ethylene/propylene sequence distribution is highly regular and uniform throughout the polymer), tend to have a flexural modulus at room temperature (25xc2x0 C.) that is higher than desired for the soft touch applications. To obtain the desired flexibility, these TPO compositions require the use of a plasticizer but over time the plasticizer migrates from the composition and this in turn, fogs the composition and/or results in a loss of impact and/or modulus. As such, a need and an interest exists for TPO compositions for use in soft touch applications that require little, if any, plasticizer.
According to this invention, TPO compositions useful for soft touch applications comprise, in weight percent based upon the weight of the composition, about:
A. 1 to about 99 percent of a least one polypropylene homopolymer or copolymer; and
B. 99 to about 1 percent of at least one homogeneously branched ethylene /xcex1-olefin copolymer in which the xcex1-olefin contains at least 4 carbon atoms and the homogeneously branched copolymer has a crystallinity of less than about 3 percent.
The polypropylenes of these TPO compositions include high and low crystallinity homopolymers and/or copolymers (e.g., propylene and ethylene), while the ethylene/xcex1-olefin copolymers are of low crystallinity, preferably amorphous or nearly amorphous. Preferably, the ethylene copolymer is a substantially linear ethylene/xcex1-olefin copolymer.
The TPO compositions of this invention exhibit unexpectedly lower modulus and/or higher impact and/or higher tensile properties then those exhibited by TPO compositions comprising a polypropylene and a conventional amorphous EP or EPDM rubber. These unexpected and desirable properties allow for the use of these compositions in soft touch applications with little, if any, plasticizer. When plasticizer is added, a smaller amount is added to the TPO compositions of the invention in order to obtain the same or better flexibility compared to prior plasticizer-containing EP or EPDM TPO compositions.